Abstract : Photooxidation of crude B. atrox asper and C. durissus durissus venom by visible light in the presence of methylene blue resulted in the detoxification of these venoms and a considerable reduction of some enzymatic activities. Immunization of rabbits with the photooxidized venoms and isolation of their gamma-globulins revealed that the immunoglobulins obtained with B. atrox asper venom did not protect mice from the effects of this venom while the gamma-globulins from C. durissus durissus animals gave a very high degree of protection. The possible cause of this discrepancy is discussed. (Author)